Method for manufacturing an electrical coil



March 1966 DHU AIRRE J. DAVIS 3,238,286

METHOD FOR MANUFACTURING AN ELECTRICAL COIL Filed March 1, 1962 2 Sheets-Sheet 1 W W 4 a2 T] T I i J ..L -J'- 942 R23 21 March 1, 1966 DHU AIRRE DAvls 3,238,286

METHOD FOR MANUFACTURING AN ELECTRICAL COIL Filed March 1, 1962 2 Sheets-Sheet 2 United States Patent 6 3,238,286 METHOD FOR MANUFACTURING AN ELECTRICAL COIL Dhu Aine J. Davis, Wheaten, Ill., assignor to Hermetic Coil C0., Inc., Wheaton, Ill., a corporation of Connecticut Filed Mar. 1, 1962, Ser. No. 176,579 2 Claims. (Cl. 264272) This invention is concerned with a method of encapsulating an electrical coil.

In some situations it is necessary that an electrical coil be sealed against moisture, and such a seal is often desirable even through it is not absolutely required. A coil which is sealed is not affected by variations in the humidity of its environment, has a longer life and has more stable electrical operating characteristics than an unsealed coil. Present coil sealing methods depend upon the impregnation of the coil with a sealing compound, as an epoxy resin. Impregnation procedures are often expensive and time consuming, particularly where it is necessary to carry the impregnation out in an evacuated atmosphere to insure that the impregnant fills all the spaces within the coil.

An object of this invention is the provision of a method for making an improved sealed or encapsulated coil in which an outer casing surrounds the coil and is sealed with the form or supporting structure on which the coil is wound.

Another object of the invention is the provision of an improved molding technique by which the sealed coil is formed.

One feature of the invention is the provision of a method for making an encapsulated electrical coil construction including a coil form, a coil wound on the form and an outer casing for the coil sealed with the form. A further feature is that the outer casing has a frictional seal with generally planar exposed surfaces of the coil form.

Still another feature is that the coil construction includes a form having a bobbin-like configuration with a coil receiving central hub and a pair of end discs, a coil wound on the hub between the end discs, with the end discs having annular portions extending outwardly beyond the coil surface, and an outer casing for the coil having a body section between the end discs of the bobbin and in intimate contact with the coil and having locking portions overlying and sealed with the annular portions of the bobbin end discs.

Yet a further feature is that the coil comprises a coil form, a coil wound on the form, terminal leads for the coil, a terminal mounting member having the terminal leads aflixed thereto and carried by the coil and an outer casing enclosing the coil and terminal mounting member with the casing being sealed to the coil form.

Another feature of the invention is the method of encapsulating a coil having terminal leads which comprises placing the coil in a mold, establishing a seal with the coil, the mold defining an annular cavity about the coil, and introducing a fluid encasing material into the mold at a point substantially on a line extending diametrically across the coil and through the point of juncture between the coil and the terminal leads therefor.

Still another feature of the invention is the provision of the method of encapsulating a coil including a winding on the form of thermoplastic material, which comprises placing the coil in a mold, forming a seal with the coil and defining a cavity around a portion thereof, heating the mold to a temperature below the softening temperature of the material of the coil form and introducing fluid plastic encasing material into the mold at a temperature above the softening temperature of the material of the coil form, whereby the encasing material physically bonds with the coil form.

And another feature of the invention is the provision of a mold for encapsulating a coil having terminal leads including at least two mating parts defining a cavity for receiving the mold to be encapsulated, the mold parts having surfaces defining a terminal lead receiving passage and having an inlet port for coil encasing material, the port being on a line extending diametrically across the cavity and through the point of juncture of the terminal lead receiving passage and the cavity.

Further features and advantages of the invention will readily be apparent from the following specification and from the drawings, in which:

FIGURE 1 is an elevation of an encapsulated coil embody ing the invention;

FIGURE 2 is a plan view thereof;

FIGURE 3 is an enlarged sectional view taken generally along the line 33 of FIGURE 2;

FIGURE 4 is a broken section taken generally along line 44 of FIGURE 3;

FIGURE 5 is a section through a mold apparatus embodying the invention;

FIGURE 6 is a transverse section taken generally along the line 66 of FIGURE 5; and

FIGURE 7 is an enlarged fragmentary view of a portion of the mold structure.

Electrical coils are often operated in an environment where they are subject to external conditions, as moisture, which may penetrate the windings of the coil and change the coils electrical characteristics or completely ruin it. With the novel coil construction and method of this invention, a coil may easily and inexpensively be sealed against external effects, and may even be operated under water.

Turning now to the drawings and more particularly to FIGURES 1 through 4, an illustrative embodiment of an encapsulated coil incorporating the invention is shown. A bobbin-like coil form 10 includes a coil receiving central portion or hub 11 having a bore 12 therethrough. A pair of disc-shaped end portions 13 and 14 extend outwardly from the portion 11 at either end thereof. The coil itself comprises a plurality of turns 15 of a suitable Wire wound about the coil receiving central portion 11 and between the flange-like disc portions 13 and 14, with the outer layer of the windings being spaced an appreciable distance, as of the order of inch in a coil 1% inches in diameter inside the edges 16 and 17 of the dis s.

The coil form is preferably of a molded plastic material, as nylon.

A pair of terminal leads 20 and 21, each having a suitable insulating covering 20a and 21a are connected with wires 15a and 15b at the ends of winding 15. The terminal leads 20 and 21 are carried by and afiixed to a terminal mounting member or yoke 23 which has a base portion 24 with an arcuate inner surface 25 that fits against the outer surface of winding 15. An enlarged or thickened boss portion 26 of the mounting member has a pair of recesses 27 therein to receive the end of the insulating coverings 20a and 21a of the terminal leads and is provided with holes 28 through which the inner conductors of the terminal leads pass.

The outer covering or jacket 30 for the coil is preferably formed, as by an injection molding operation to be described below, of a suitable insulating material. For example, the covering may be of the same nylon material as the coil form. The outer covering 30 has a main body portion 31 lying between the peripheral extensions of the bobbin end members 13 and 14. Annular cover portions 32 and 33 overlap the edges of the bobbin end members and interlock therewith, forming a tight mechanical seal. This seal or interconnection between the cover 30 and the coil form holds the two parts together and prevents the entry of moisture or other undesired contaminating materials. The cover 30 also seals about the insulating covering 20a and 21a of the terminal leads.

For many uses of an electric coil, the mechanical interlock between the encapsulant body and the coil form is adequate. However, where necessary, a physical bond may be provided by utilizing the proper temperature conditions during the molding operation, softening the coil form material so that the cover bonds with it.

Referring now to FIGURES 5, 6 and 7, a suitable mold for encapsulating the coil of FIGURES 1 through 4 is shown. The mold includes an outer mold member or block 35 shown resting on a surface 36. The mold is in two parts, 35a and 35b which mate along a separation line 350. Extending through the mold is a centrally located bore 37 in which two further mold members 38 and 39 are slidably received. Mold member 38 comprises a cylindrical portion 38a filling the lower portion of bore 37 and having a centrally located upstanding rod portion 40. Mold member 39 is generally cylindrical in cross section and fills the upper portion of bore 37, having a central passage 39:: in which rod portion 40 is received.

A coil to be encapsulated. is inserted into the cavity of the mold, between the upper face 38b of the cylindrical portion 38a of the mold member 38 and the lower face 39b of mold member 39. The terminal leads 20 and 21 of the coil extend outwardly through grooves formed in the mating faces of mold parts 35a and 35b as best seen in FIGURE 5.

The coil to be encapsulated, i.e., the coil form and winding, is positioned in the mold cavity defined by the bore 37 through mold parts 35a and 3511, the upper face of portion 38a of mold part 38 and the lower face of mold part 39. The upper surface of portion 38a of mold part 38 sealingly engages the lower face of bobbin end member 14, while the lower face of mold part 39 sealingly engages the upper surface of bobbin end member 13. The respective upper and lower faces 38b and 39b terminate inside the peripheral edge of the bobbin end members, the mold parts forming annular channels 43 and 44, one associated with the bottom of the coil and the other with the top, within which the annular cover portions 33 and 32 are formed.

Encapsulating material is introduced into the mold cavity through a passage 46 which enters the mold cavity at a point substantially on a diameter of the coil passing through the point of juncture between the coil and the terminal leads therefore. The fluid encapsulating material flows around the coil in each direction and forms a solid body filling the mold cavity. The diametric relation between the inlet port and the coil terminals allows the material to flow evenly about each side of the coil, without obstruction of one path more than the other by the terminal leads and the terminal mounting srtucture. Where the encapsulating material may have a tendency to lift the ends of the terminal mounting yoke 23, the inlet passage is preferably located immediately adjacent the terminal lead structure, as shown in broken lines at 46'.

The encapsulating material, which may be a suitable thermoplastic material, as nylon, is introduced into the mold from a heating chamber (not shown) through a connector 47. The heating chamber and material feeding apparatus may be of any suitable construction.

In accordance with the invention, the winding is placed on the coil form in the usual manner by a suitable winding machine. The terminal leads and 21 are mounted in yoke 23 which is then secured to the surface of winding 15, as with a double-faced adhesive tape, or other suitable adhesive material. The ends 150: and 15b of the winding are then mechanically and electrically connected with the conductors of the terminal leads 20 and 21. The coil is placed in the mold cavity and the mold parts assembled as shown in FIGURE 5. Liquid encapsulating material is then introduced into the mold under suitable conditions of temperature and pressure, to form the jacket 30 around the coil. As thermoplastic materials have a tendency to shrink slightly upon setting, a firm mechanical bond is achieved between the jacket casing, the coil support and the winding itself. If a physical bond between the encapsulating material and the coil form is desired, the temperature condition within the mold should be such that the coil form is softened upon the introduction of the liquid encapsulating material. Where necessary, the mold itself may be heated as by an electric element 50 carried in one of the mold parts.

It is important that a good mechanical seal be maintained between the mold parts and the coil support during the encapsulating operation, to prevent excessive flashing of the encapsulating material.

Where nylon is used as the encapsulating material, and it is desired to achieve a physical bond between the encapuslating coating and the coil support, the temperature of the mold should be of the order of Fahrenheit during injection. The injected molten nylon may have a temperature of the order of 500 Fahrenheit, the heat of the mold and of the molten nylon softening the bobbin, allowing the bobbin and covering to bond together. After the mold cavity is filled, it is allowed to cool, completing the bond between the covering and the coil form and causing the coating to shrink tightly about the winding 15.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. The method of encapsulating an electrical coil wound on a bobbin coil form having a central hub with two ends and a disc shaped end portion at each end of the hub, said coil being wound about said hub with the outer surface of the coil exposed between said disc shaped end portions and recessed within the periphery thereof, the coil having a pair of terminal leads extending outwardly from the coil surface between the end portions, which comprises: placing said coil in a mold; establishing a seal between the end portions and the mold, said terminal leads extending generally radially outwardly from the coil surface between the bobbin end portions and in a plane generally parallel with the end portions; and introducing a fluid encasing material into said mold under pressure at a point spaced from said end portions, coinciding with the intersection of the mold and a plane extending diametrically through the coil at right angles to said end portions and through the point of juncture between the coil and said terminal leads but said point not coinciding with said leads, the fluid encasing material dividing and flowing in two paths around said coil, substantially without obstruction, to fill the annular space substantially without flowing past said terminal leads and without establishing a back pressure which would disarrange said coil.

2. The coil encapsulating method of claim 1 wherein said terminal leads are secured to an arcuate mounting member having a convex outer surface positioned against the outer surface of said coil and the fluid encasing material is introduced into the mold at a point axially spaced along the coil from the plane of said leads, adjacent the terminal mounting member and directed against said convex outer surface of said mounting member.

(References on following page) 5 References Cited by the Examiner 2,882,504 4/ 1959 UNITED STATES PATENTS 3 323 333 12/1919 Milton 18-59 2 956 31 10 19 0 8/1945 Brink 1859 5 2,975,481 3/1961 12/1951 Giacomo 264272 3 45 0 1 /1954 Firth 1859 3 077 003 2 19 3 11/1955 Merrill et a1 18-36 3/1958 Chapman et a1 264328 10/1958 Forest et a1. 18-59 11/1958 Golbert et a1 33696 3/1959 Crarner 1842 Hultgren 336-96 Harrington 264-272 Herbst 18-59 Naimer 18-59 Kaufirnan 1842 Anderson et a1. 1859 Hobson 1836 ROBERT F. WHITE, Primary Examiner.

10 JOHN F. BURNS, ALEXANDER H. BRODMERKEL,

Examiners. 

1. THE METHOD OF ENCAPSULATING AN ELECTRICAL COIL WOUND ON A BOBBIN COIL FROM HAVING A CENTRAL HUB WITH TWO ENDS AND A DISC SHAPED END PORTION AT EACH END OF THE HUB, SAID COIL BEING WOUND ABOUT SAID HUB WITH THE OUTER SURFACE OF THE COIL EXPOSED BETWEEN SAID DISC SHAPED END PORTIONS AND RECESSED WITHIN THE PERIPHERY THEREOF, THE COIL HAVING A PAIR OF TERMINAL LEADS EXTENDING OUTWARDLY FROM THE COIL SURFACE BETWEEN THE END PORTIONS, WHICH COMPRISES: PLACING SAID COIL IN A MOLD; ESTABLISHING A SEAL BETWEEN THE END PORTIONS AND THE MOLD, SAID TERMINAL LEADS EXTENDING GENERALLY RADIALLY OUTWARDLY FROM THE COIL SURFACE BETWEEN THE BOBBIN END PORTIONS AND IN A PLANE GENERALLY PARALLEL WITH THE END PORTIONS; AND INTRODUCING A FLUID ENCASING MATERIAL INTO SAID MOLD UNDER PRESSURE AT A POINT SPACED FROM SAID END PORTIONS, COINCIDING WITH THE INTERSECTION OF THE MOLD AND A PLANE EXTENDING DIAMETRICALLY THROUGH THE COIL AT RIGHT ANGLES 